US2692048A - Method for sink and float mineral separation - Google Patents

Description

Oct 19, 1954 DAVIS 2,692,048

METHOD FOR SINK AND FLOAT MINERAL SEPARATION Filed Sept. 25, 1950' T- 2 'Jnven zar Lg)"; E J e .9022 17 9032115 4 I I": i 5 a v 40 L. J

Patented Oct. 19, 1954 METHOD. FOR. SINK AND FLOAT MINERAL SEPARATION Nelson L. Davis, Chicago, Ill. Applicationseptembcr 25, 195.0, SeriaLNo. 186,604

6 Claims. (01. 209-4725) My invention relates to improvements in means for controlling the density of. the mediumor bath in a float and sink mineral separation apparatus and process.

By sink and float separating method and process, I mean a method and apparatuswhere solids,

suchas coal or ore asit comes from the mine, are

fed to a bath of liquid, the specific. gravity of which is greater. than. some ofthe solids and less than others, sothat theslight solids may float on the surface and the heavy solidsmaysinkto the bottom, the float. andsink solids beingseparately discharged.

My invention is especially useful in the. treat-- ing of coal, ore and the like, wherein the medium, consists of water with finely divided magnetite, flue dust or other magnetizable media maintained in suspension therein by constant circulation.

Assuming a media of predeterminedsize-and consistency thev rateof sinkage in water may be established. In order that the-eifective-specific gravity or density of the medium-may be maintained constant, it is then necessary to first insure the use of the heavy media inthe. waterrat substantially constant particle. size; to maintain a uniform amount .or weightof media in the waterand to circulate'the water and media at a .sufi'iciently rapid rateto insure that the media will remain insuspension inthe Water. The. effective specific gravity of the medium may beset and controllediin consonancewith the separation of float and sink solids desired. The lower the density of the medium the larger will be the. proportion of the solids which will sink, so if it is desired to obtain coal'for metallurgical purposes of the highest purity, the specific gravity might be.v set and held at- 1.35; Under these circumstances only purer coal would float, everything else, including bone coaland contaminated coal, would sink. If, on the-other hand, the object were to obtain coal where maximum purity was not essential, the specific gravity of the medium might be. keptat 1.60. Under these circumstances-all the pure coal would float and some of the coal which -.was ballasted with foreign matter, such as sulphur and the like, would sink in the first case, would now, because of: the increased density of the medium, be recovered with the coal.

Thus, it is of the utmost importance that the specific gravity of the medium be accurately controlled and it is of equal importance that during the entire time of operation of the bath, the specific gravity or density remainconstant without local or. periodic changes. in .density.

After. the. sinkand float .separation has been ac.-

complished in the vessel or bath, then the sink.

and float material isseparately discharged. Usually the float material flows over a Weir with some of the medium.v Usually the sink material is. mechanically raised above the levelof the bath, partially drained,.and then it is discharged. In any case, a certain amount ofthemedium leaves the vessel with both the sink and float material and so both the liquid andthemedia orv suspension solids must be returned to thebathn In order to recover. not merely the media in suspension in: the. water as it leaves the vesselwith the recovered solidsbut also tov recover the media adhering to the solids and not drained off,

it is customary to wash or. rinse the discharged solids after they have. been. drained, the. rinse water taking away from the solids. the residual media and thus containing in great dilution, media which should be returned to the system.-

Inthe past, it has been customary to. discharge the medium drained off from the solids, together with the. rinse or wash water into a: large reservoir or settling tank where the diluted medium may-be, by sedimentation-or other treatment, concentrated for return with some water to the circulating system. so asto maintain constantdensity.

This requiresexpensive installation,. requiresthe pumping and storage of a relatively large amount-of water, ,requires thexprovision of a-rela tively large amountofthe expensive media not. actually in use in the suspension.andrequires exceedingly careful control to insure that the. con-- centrated medium recovered: by sedimentation is returned to. thesysteminconsonance with: the proper amountof water to give the'desiredconstant .density.

I propose to avoid all thesediflieulties by aconstant and continuous circulation, by returning to the Vessel-Where theseparation takes-place,,all or substantially-all'of the withdrawn media, doing it as a. part .ofa continuous-prooessFso thatthere is a-continuous .circula-tion of the liquid with the media in suspension:

To the extent'that I return immediately to the circulation systemthe water and. media-Which leave the systemwithtreated solidst to that extent I-obviate the-necessity; of accurate control. If you put back in exactly the-same amountzofrwater and media as you take out, there can be no change in density. Thatisxnot one hundredxpercent-possible. but itis possible to closely approach this situation.

The. solids introduced in the system: contain inevitably a-certain amount of -fine material.-- As 3 the solids pass through the system, degradation takes place and there is, therefore, added to the bath a continuing supply of fine, non-magnetic material which passes through the screen and is washed off the solids with the magnetite and returns to the circulating system. Means must be provided for removing these non-magnetic solids. To do this I propose to pass the rinse water, containing both magentic and non-magnetic solids, through a continuously operating magnetic separator. The magnetic separator will operate on a relatively dilute feed slurry which will always be uniform with respect to the liquid volume forwarded to the magnetic separator. The water carrying non-magnetic solids are discharged from the float and sink system, and a relatively thick concentration of magnetically recovered solids will be continuously returned to the system. The amount of water in the rinsing process is constant, the amount of water discharged with the non-magnetic solids from the magnetic separator is constant and the amount of water returning with the magnetically separated media is constant.

The amount of water permanently withdrawn from the system adhering to the float and sink materials discharged and the relatively small amount of media not rinsed off these materials may both be determined.

With all these factors in mind, it then becomes possible to determine just how much additional media must be added to the system and just how much additional water must be added to the system to maintain constant conditions and experience has taught that the amount of water and the amount of raw media needed may be accurately determined and the amount required by day by day operation is small enough so that easy, satisfactory operation may continue and the discharge of non-magnetic finely divided solids by the magnetic separator is sufiicient to maintain the concentration of non-magnetic finely divided solids in the bath below the point at which they interfere with proper sink and float separation.

The magnetic concentrates are thus continuously recovered and returned to the pump sump at the same rate that they are removed from the surface of the float and sink products discharged from the float and sink bath. As a result, there is a substantially unvarying concentration of the media in the separating tank, and the specific gravity of the medium never changes by more than the amount of medium that escapes from the system with the float and sink products, or from the magnetic separator. Therefore, only that amount of media necessary to replenish the irrevocably lost media needs to be supplied.

The medium drained from the treated solids may be returned directly to the circulating system or may be returned to the circulating system through a magnetic separator. The same is true of medium recovered by the rinse water. The magnetic separator suitable for use with my invention is of a type which works best on a thin slurry and continuously recovers a highly concentrated magnetic media product for continuous and immediate return to the circulating system.

4 There is no sedimentation tank and no delay while sedimentation takes place. There is no treatment of the magnetic media except by the magnetic separator, which inherently discards non-magnetic solids, recovers and at the same time densifies and returns the magnetic solids.

If desired, the feed slurry to the magnetic separator may be magnetized to assist the magnetic separator to recover magnetic solids. Such premagnetization is, however, not always essential.

If desired, the media discharged from the magnetic separator may be de-magnetized, as it is returned to the system.

To be sure, Ido have a small sump below the separating vessel into which the medium flows and from which it is pumped back to the vessel. This sump, however, has nothing to do with the operation of the devicewhen it is working, being, in effect, except when the plant is shut down, merely a part of the liquid conduit system. The purpose of the sump is to provide a sufficient capacity to hold the contents of the vessel and the circulating conduits when the power is turned off and the vessel stops work. The size or volumetric capacity of the sump and the vessel and the conduits is such that at the rate of discharge or fiow through the vessel, there is a continuous flow of the medium. The pump circulates the medium through the system at a rate such that the entire liquid content of the system is replaced every two minutes or less and settling in the sump during operation is entirely prevented.

Other objects will appear from time to time throughout the specification and claims.

My invention is illustrated more or less diagrammatically in the accompanying drawings, wherein- Figure 1 is a horizontal flow sheet; and

Figure 2 is'a vertical flow sheet.

Like parts are indicated by like characters throughout the specification and drawings.

The details of the mechanisms themselves are indicated diagrammatically as the particular mechanisms are well-known in the art and form no part of my present invention.'

i indicates the raw coal supply. It may be a conveyor or a chute or any other desirable mechanism. This raw coal is discharged across pre-wet screens 2. These pre-wet screens eliminate from the system under-size solids which are adapted to be treated by other methods. For example, the screen will pass 0.25 inch, so only plus 0.25 inch material enters the float and sink system and minus 0.25 inch solids are discharged along the line 3 to any suitable point forming no part of the invention.

4 is a head tank, water being led from that tank along the conduit 5 to be sprayed on the coal as it passes over the upstream part of the pre-wet screen. The screens beyond the sprays dewater the raw material under such controlled conditions that the surface water carried into the separating system by the raw material will be constant and uniform throughout operation. As will' hereafter appear, this is important because the relationship between the surface water on the solids leaving the system must be so controlled that more water leaves the system than enters it. The mixed coal and refuse in moistened though dewatered condition is discharged along the conduit 6 to the heavy medium processor 1, where the sink and float separation takes place. The float coal is discharged from the processor over the wei a and chute e "to the float screen 10. rh'ejsini; material raised from the bottom or the pr ce'ss'or vessel "isdisch'a'rged via th'echute I l ftp thesinkscr'e'en l2. In this case, I have illustrated two processors, two float screh'syea'ch onereceivin'gjthe discharge from one of theprooessors and a sink screen which receives the refuse from both. Since in coalthe amount "of refuse fis'small in proportion to the amount of coal, this is a suitable arrangement. The chutes 9 and are provided with fixed screens 13 and I4, the screens themselves being preferably vibratory screens. The fixed 'scr'eens l3 and I4 and the upstream'end of the vibratoryscreen's are located over hoppers l5. The downstream'ends of the screen-s19 and 12 are located over hoppers [6. Water fro'rnthe head tank l"discharg'ed 'throughthe'conduits ll isfsprayed at [8 onto the sink and float material on the vibratory screen's so that the drainage Jmedium'with media in suspension therein passes to'the hoppers l5 and the rinse water, sprayed ontothe solids'after they have passed down the vibrating screens a short distance, passes into the hopper l6, carrying With it the media Washed off the solids after drainage.

The final rejects, that is the sink "material, passes out for-discharge along the chute or conduit IQ and the coal is discharged along the conduit 2! as a clean product, both the reject and thecoalh'aving been washed so that they carry "away from the system a minimum of adhering media andsince the coal and refuse are drained before they are'rinsed, the volume of Water carriedaway from the main circulating system by the solids is slightly greater than the volumeof water brought into the system with the solids 'fromthe pr'e-wet screens.

2| is a heavy medium sump. It receives medium from the hoppers I5, along'the conduits 22 and the pump '23, withdraws the medium from the bottom of the sump,discharges it along the conduit "24, to the processor. The conduit 24 divides before it'reaches the processor and 25 conducts medium toward thebottom' of the processor where'it is fed in through a diffuser plate 26 and the conduit 2 conducts some of the medium to the'side of the'processor where it is fed in over a diffuser plate 21a substantially at the surface of the bath but'the medium fed by the pump to the processor is the same in' character whether it. goes in at the'bottom or at the side.

The'specificgravity of the medium drained off the coal is the same as that of the medium in the "sumpan'd in the processor. It merely circulates continuously through the system. The rinse water received in thehoppe'r Hi contains media finsuspensi'on but the quantity is so small that the Specific gravity of the rinse water is far below the 'specificgravity of the medium circulated in the system'so that rinse water containing, as it does, a'small amount of magnetite or other media and also containing fine dust, dirt, degradation products, etc., passes from the hopper i6 along the duct'23 to the magnetic separator "29. pence moving in the direction of the arrows, immediately above "a magnetized member 3|. The water'withmedia and refuse'is discharged againstthis belt. The magnetic efiect holds the media'against the belt as the belt moves upwardly. The water and non-magnetic solids flow down the *belt -andare discharged from the hopper 32, the amount of Water bearing such relationship to the f water received'by the magnetic separator that "tlie magnetitewhich passes up over the belt and Themagnetic separator in this case has a:

v is; dischargedihto'the 33 is a cease-emcee.- The dischargeto the magnetic separate-rename discharge from the bottom of the separator very dilute but the -recovered magnetite is relatively more dense than the medium circulating through the system. 11; discharges irearms hop per 33 through .deniaghetiz ing coil 34 to the heavy medias'ump 21. Under 's'ome circum stances, thedemagnetiaing coil is not 'n'e'ded and the magnetic separator may discharge directly into the sump 2|. -If desired, in order to mcre rapidly get 7 rid 6f "n'on magn'etic -solids, the discharge from the happier '15 may a1so be fed to the magneticsparator. The magnetite-in either case willfbe recovered. The non-magnetic fine solids will be discharged.

The s stem is thus'a nominally closed system in so far as the suspens'idnhediuin is concerned. The suspension medium "circulates continuously either direct to the sum, the pump and themeses'sor or by-pa's's ed through the magneticseparator. In either case, their e is'a constant flovfof medium or water and-media are urrir-onnaateor speed and there is no place in the system Where new is interrupted, "or delayed, 50 thedensityhf the medium will remain constant. The 'fonly exception tothis being, of course, the very small amount of-media which adheres to the coal and refuse and is carrid out of thefsystem'andthat lost in the discharge produ'ctbf the magnetic separator. Since this dependsonthe character and size of the coal and since'the'characte'r and size of the coal does not normally vary, this amount can easily befdetermi'ned and it is only necessary to add additional magnetite to; the system in consonahce wi'ththis rateof wastage. Since the feed coal is pr'e-we't and then 'de'watere'd Before ent'erir'ig the processor, but only" drained and notdewatered until after being rlnsed,y; ater is're'moved on -the surface of the float and sink pfoducts at a grea t'er rate than ehterdwiththe feed to the processor. Therefore, the-effct i's one which always requires waterto be replenished to the medium to holdits density constant. Thus, I am able to have a continuously operating device wherein the specific gravity or density of the medium may beset and controlled and remain constant during the operation-of theapparatus.

Ihe liquidfrom the magnetic separator32 discharges through the piped! to the clarifying basin' lil. The water fed to the clarifyingbas ih fill from the pre watering screen contains finely divided solids, small enough to pass'through the screen. The Water discharged from the magnetic separator contains degradation products from the system mostly non-magnetic though, of course, there is always the possibility of escape of some of the fine magnetic solids washed off the coal and refuse discharged from the float vessel.

These solids settled to thebottom' of the tank are collected in the usual manner by any suitable collecting means indicated in dotted lines as '42 and are discharged through the passage 43 to waste or to other treatment means forming no part of this invention. The clarified water overflows in the usual manner into the hopper 44, is returned by'the pum 45 through the conduit 4 to the head tank 4.

Thus there are two separate nominally closed liquid circulating systems, one including the vessel, the sump, the pump and the associated conduits through which the flotation medium is circulated, the other, the water system including the head tank, 'the'sprays. the run as fromthe dewatering screens 2 and from "the magnetic were separator 32 so that there is a continuous circulation and clarification of water to and through the head tank.

The cooperation of these two circulating systems is of the utmost importance. If, for example, less. water is removed from the medium in circulation than is brought to it on the surface of the pre-wet feed material, a diluting effect results. To compensate, it would be necessary to be continually adding make-up magnetite to hold the density at constant level. The liquid volume contained in the system would always be expandin and the result would, of course, be intolerable.

Also, if we only remove from the medium an equal amount of water to that entering it on the surface of the feed material from the pre-wet screen, then under these circumstances, the balance would be so closely drawn that the difficulty outlined above might be experienced. This, therefore, is also an unsatisfactory condition.

The only permissible condition is that where more surface moisture is removed from the medium than enters with the feed from the prewet screen. With our flow sheet this is obviously the case since the length of the pre-wet screen beyond the wetting sprays is used for the purpose of dewatering the feed. As the float and sink products are removed from the bath in the processor, the same opportunity for efficient dewatering does not exist prior to the point of reading the rinsing sprays. In other words, drainage of the surface moisture is less complete at this point of travel than at the discharge end of the pre-wet screen. This, then, results in a condition where more surface moisture is removed from the medium than is discharged to it and this results in a shrinkage of volume for the medium in circulation, which must be replenished by make-up water. Since the dense concentrates from the magnetic separator also contain some water, the net amount of make-up water needed results from the equation:

Exit H2Oentering H2O=H2O in magnetic separator concentrates+make-up water From this it can be seen that if the make-up water should have become a minus quantity we would be in serious trouble because we would need to be continually adding make-up magnetite to prevent the sump medium from being diluted. This would result in th expansion of liquid volume which would defeat our purpose.

The surface moisture contained on the dewatered float and sink products at the discharge end of the rinse and drainage screens should be approximately equal to the surface moisture contained on the feed material discharged from the pre-wet screen. The only effect of this is in connection with the amount of makeup water required for the circuit between the head tank 4' and the clarified water from mag netic separator discharge hopper 32 which is returned to the head tank 4 in closed circuit.

I have diagrammatically illustrated a magnetic separator. Any type is suitable which will effect a continuous separation of the magnetite from the water and solids and return this directly to the system.

The sump 2|, while big enough to hold the entire capacity of the system when the system is closed down and no water is circulating, is practically empty during operation so that there is a continuous flow to and through the sump and the sump merely acts as a conduit for such continuous flow.

I have not illustrated any particular mecha nism for adding the small amount of magnetite needed to compensate for that which finally escapes from the system nor have I illustrated any particular mechanism for adding the small amount of water necessary to keep the system filled for operation, since the details of these form no part of my invention. 7

While the dewatering screen operates mechanically to feed raw solids to the bath with a generally uniform amount of surface moisture, it will be obvious that the actual volume or weight of surface moisture fed to the bath with the raw material in any given increment of time will vary in consonance with variation in the size of the particles.

The smaller the particles, the larger the superficial area per pound or ton of the raw material and the more surface water carried in with'the solids. The dewatering screen mechanically removes this surface moisture to the point that the amount of moisture on the surface of each particle is generally uniform.

Also when the solids are discharged from the bath, the actual volume of surface water varies in exactly the same way in consonance with the size of the particles but since the particles travel through the bath at a very high rate of speed, perhaps only a few seconds being required for the particles to enter the bath, be gravitationally separated and discharged, the conditions both at the intake and at the discharge with respect to the amount of moisture are generally uniform.

It is conceivable that in any given small increment of time there might be a wide range of variation. For a few seconds or even for a minute most of the coal might be in very large pieces. Then suddenly in the next few seconds or minutes, the coal might be all in small pieces. Under these circumstances there Would be a considerable change in the amount of moisture entering in and taken from the bath but that chang is in consonance with this change in size of particles. It is a fact that in any long period of time the sizes of the particles average out but it is essential that the bath' density remain constant. It is not sufficient that it average out over a long period of time. It must remain constant at all times and my arrangement whereby I introduce a controlled percentage of surface moisture and discharge from the bath the solids with a controlled percentage of surface moisture somewhat greater than that percentage which entered, makes it possible for me to maintain long averag densities over a long period of time but substantially constant density at all periods of time because of the immediate return to the bath after the screening and draining and also after the magnetic separation of the magnetite drained off and rinsed off of the individual particles. This would not be possible were I to use in the system a densifier or a clarifieror any other means which retained the magnetite for a continuous time consuming treatment and therefore one of the most important elements in my invention is the fact that the medium drained from the solids is immediately returned for circulation in the bath and the medium rinsed from the solids is immediately and continuously concentrated by the magnetic separator and immediately returned for recirculation in the bath.

The use and operation of my invention are as follows: 7

The achievement ofa float and sink separation for minerals such as coal has been successfully lishs by us n Simh'susp ns'io l .i a ent oe the bath? T e r ul .h t art cl s h vin a l ss d nsity ha 'the b h will "flo t w ile th'o e'hav n' asrea 'e de si w l'sink- One of the practical problems, incidental to the com jiercial useof such a fioatfands'ink process is wa er m in a n n th a h at n n density examp con the'ca' e f tr ats aw. c al. an n m siz etweent i limits o n he avera e siz of the artic s." i l va "from" m nut to m n e and so" the exposed surface area ofFthe' feedmaterial constantly'varies between Wide limits, yet; over the p ri d o p haps One; our thej'ayera e suri c' area' i o lrequa to the ave'reee ui a fe a e of feed material'during anyfoth'er hour. There fo e th dens .oi the bath must e 'cgn re d on a minute to minute rather; than nan hour to hour hasig c, r,

he e materi enters t b th th W t r o i s xp sed's iaces tw hen' emoved from the 'bath,'"retain' on those surfaces hoth liquid and suspended'solids; Iuot'henwords, it Will remove m e bath inelis ien ich wer not present when the feed entered the bath and the rate of such. removal varies in prop ortionto the extent of variation of surface'area. The drawin'gja ffiow'sheet, shows diagrammatically the Operation of iny inventioni" "Bearing in mind that the two ingredients or the bath are water and solids, it willhe clearly apparent that water and solids removed from the bath ori'thesurface of the float and products must be returned to the bath in e ual amount and a n Eq alen K to h 'o the r' remova if the density or" the bath is to be kept constant.

First, consider the one ingredient-water. To establish a uniformaver age of surface moisture of raw feed'coal entering the bathflthe co "is first wet with sprays of'wate'r and is then" rnechanically dewa'tere'd by means'of aprewetting and dewatering screen. After immersion'in'the bathythe float and sink solids are evacuated and drained. Freelydrainingwater is'returne'd immediately to the bath but before mechanical dewatering has been'accornplished over the drainage screento'" the excent'thst it was accomplished with the prewet screen. It is, therefore,

established that less water will be restored to the :Qfir han PFW 0! the fee tfili i new? vb h Next/consider the solids. ,We are only concerned. with solids that ar magnetically "susceptiblelhecause my bath is comprised git-water a i s e iqa ly susqep le sol Since :n magnetic solids are on the surface of the raw feed coal entering the bath but are retained on the surface of the floatandsink solids'deaving the bath, there are onlyitwochannels through which such magnetic" solids can"be"re'covered and restored to the bath." "The fiist"of"these channelsmay be considered as theliquid which drains freely from the float and sink solids and which returns directly to the sump for imm diate recirculation These" liquids are as ntially of the same density as the bath liquid. The second channel consists of the rinsing of the float and sink products after they have traveled beyond the zone where free drainage occurs. Here, Water is used for rinsing purposes and the magnetic solids thus recovered must first be separated from water and any non-magnetic solids present by means of a magnet. The magnetic concentrates are discharged oontinuousiy and this m be iqll w ii d red n em litl zet nw i "b i. tur d 91' he"b,ai m' h the ,um 'Pbnt 'd u th the rate bi rs lame i n "of ma h Solids" by 5 rinsing'ds a variahle that 'is a function of the s rface area of the float sink' products. Since" the bath" density must he "maintained as a q nst itw l' e de rly e dent h th can be c'cd plished f th a n i s j ered yfrn insi'z nd m gn iiisf a are et'jf eu to "the "bathwithout any lossof time ub equent to h reniq a xfro 'th at The lisert an d timeheti enre o and; r tur the" greater? thevairiation of bath density, which is'an in ia peratin it Qni wso thi r b m ve some wh h nsu i t m lag q fo i 110 .1 Qfmmi etwe n t e e" sqli e 1 removed rom the b th -1. 1 t nsd 'i My invention pe'r n'lits thijs'time interval to he ifl l d" 2Q le 12 PM m te n $1 f i i "i c ve ar 'is mp fie to he x e t" h only amagneticseparator isinvolved of a type which will alsodischarge magnetic concentrates having a; density materially greater than the density oi the b'ath; "Thus, it is always necessary 'jfor the operator to'add'water which is lost in the circyit never necessary to add magnetiteto oifsetthereturn of concentrate which is of l 1en$ ty t the-b or f s amount usly efine removed'from [the than 150 2 hath: Itflis, of course, understood that the system continuo sl '1 "'s a c 'rt m unt m net ie ec seu s eilis n r' r ry is n Qiie"hundreslrersent ut th un O meenetite" replenished*"needs only to be equal to that lost due ,tosomet hingless than one hund ed sc eam 'ificiei o 're v' ry.

1. The method of sink and float separation which "consists in, screening wet raw" some to eliminate'the' fines, 'dew'atering the raw solids to u fgrm mo nt of surf c m t re e n a bath containing suspension mec. bfw tre d n y dm netic media ulat'edto, through marrem the bath atsuchratethfat the mediarein'ain in s san epa at Wit d w n th i k a serg -r am the "bath with Sorrr'eof the medium; seeming the solids and returning, for immediate circulation through the bath, the merain'ed from the sjblids, the screeningleavg th s idswith in re surface moisture than was foil theinwhen they entered the bath, rinsing on 1 treatment directly to magnetic separation, recovering returning "the magnetic media with a relatively small amount of water as 'ajthickconcentrate directly without any treatn ct I "than magnetic separation to the hath circulating s'y'st emf' 2. The method of sink and float separation whichton'sists in, screening 'wetraw sense to eliminate he fine's,'dewatering' the raw solids to "eiu'n Writ o urfac o st re tr a n the'sohds in a bath containifiga eu'epeneienmedium consisting of water and finely divided magnetic media circulated to, through and from the bath at such rate that the media remain in suspension, separately withdrawing the sink and float solids from the bath with some of the medium, screening the solids and returning, for immediate circulation through the bath, the meleaving the solids with more surface moisture .than was on them when they entered the bath,

rinsing the drained solids, dewatering them and subjecting the resultant thin slurry without any additional treatment, directly to magnetic separation, recovering and returning the magnetic media with a relatively small amount of water as a thick concentrate directly without any treatment other than magnetic separation to the bath circulating system, clarifying the water discharged from the magnetic separator and reusing the clarified water to rinse the solids.

3. The method of sink and float separation which consists in, screening wet raw solids to eliminate the fines, dewatering the raw solids to a uniform amount of surface moisture, treating the solids in a bath containing a suspension medium consisting of water and finely divided magnetic media circulated to, through and from the bath at such rate that the media remain in suspension, separately withdrawing the sink and float solids from the bath with some of the medium, screening the solids and returning, for immediate circulation through the bath, the medium drained from the solids, the screening leaving the solids with more surface moisture than was on them when they entered the bath, rinsing the drained solids, dewatering them and subjecting the resultant thin slurry without any additional treatment, directly to magnetic separation, demagnetizing and returning the magnetic media with a relatively small amount of water as a thick concentrate directly without any treatment other than magnetic separation and subsequent de-magnetization to the bath circulating system.

4. The method of sink and float separation which consists in, screening wet raw solids to eliminate the fines, dewatering the raw solids to a uniform amount of surface moisture, treating the solids in a bath containing a suspension medium consisting of water and finely divided magnetic media circulated to, through and from the bath at such rate that the media remain in suspension, separately withdrawing the sink and float solids from the bath with some of the medium, screening the solids and returning, for immediate circulation through the bath, the medium drained from the solids, the screening leaving the solids with more surface moisture than was on them when they entered the bath, rinsing the drained solids, dewatering them and subjecting the resultant thin slurry without any additional treatment, directly to magnetic separation, recovering the magnetic media, demagnetizing and returning them with a relatively small amount of water as a thick concentrate directly without any treatment other than magnetic separation and subsequent de-magnetization to the bath circulating system, clarifying the water discharged from the magnetic separator and reusing the clarified water to rinse the solids.

5. The method of sink and float separation which consists in rinsing and screening raw solids to eliminate the fines, dewatering the raw solids to a uniform amount of surface moisture, treat- 12 7 ing the solids in a bath containing a suspension medium consisting of water and finely divided magnetic media circulated to, through and from the bath at such rate that the media remain in suspension, separately withdrawing the sink and float solids from the bath with some of the medium, screening the solids and returning, for immediate circulation through the bath, the medium drained from the solids, the screening leaving the solids with more surface moisture than was on them when they entered the bath, rinsing the drained solids, dewatering them and subjecting the resultant thin slurry without any additional treatment, directly to magnetic separation, recovering and returning the magnetic media with a relatively small amount of water as a thick concentrate directly without any treatment other than magnetic separation to the bath circulating system. 7

6. The method of sink and float separation which consists in, rinsing and screening raw solids to eliminate the fines, dewatering the raw solids to a, uniform amount of surface moisture, treating the solids in a bath containing a suspension medium consisting of water and finely divided magnetic media circulated to, through and from the bath at. such rate that the media remain in suspension, separately Withdrawing the sink and float solids from the bath with some of the medium, screening the solids and returning, for immediate circulation through the bath, the medium drained from the solids, the screening leaving the solids with more surface moisture than was on them when they entered the bath, rinsing the drained solids, dewatering them and subjecting the resultant thin slurry without any additional treatment, directly to magnetic separation, recovering and returning the magnetic media with a relatively small amount of water as a thick concentrate directly without any treatment other than magnetic separation to the bath circulating system, clarifying the water discharged from the magnetic separator, and reusing the clarified water to rinse the solids.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,135,957 Wwensch Nov. 8, 1938 2,151,175 Wwensch Mar. 21, 1939 2,206,980 Wade July 9, 1940 2,325,149 Rakowsky July 27, 1943 2,387,866 Walker Oct. 30, 1945 2,490,365 Lowe Dec. 6, 1949 2,496,590 Marsh Feb. '7, 1950 OTHER REFERENCES 11 and 12.

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